UPPER CHALK FORMATIONS. 



sometimes it is o'olitic in character, and becomes almost crystalline 

 even magnesian, and in localities remote from crystalline materials 

 which might affect it. The inferior part of this formation is fre- 

 quently soiled with clays chalk marl. Above it is more pure, 

 and contains a great many nodules of flint or silex. Though this 

 character is very common, it is wanting in a great many places. At 

 its upper part the chalk formation becomes very sandy, as in the 

 neighbourhood of Maastricht. 



16. Excepting the ba'culites found at Maestricht, the remains 

 of cephalopods are not found in the upper creta'ceous formation ; 

 but belemni'tes (from the Greek, belem'non, a dart) of particukr 

 species, such as Jig. 138, and many other organic remains not 



Fig. 138. Belemni'tes mucrona'tus. 



met with in the chalk marl, are found : among them are the pla- 

 gio'stoma spino'swn (Jig. 139) ; the o'strea vesicida'ris (Jig. 140) ; 



Fig. 139. Pla gio'stoma spino'sum. Fig. 140. O'strea vesicula'ris. 



the Ca'tylus Cuvieri (Jig. 141), the structure of which is fibrous ; 

 the Terebra'tula Defra'ncii (Jig. 142) ; the ana'nchytes ova'tua 

 (Jig. 143) ; the Spa'tangus cor-ari guinum (Jig- 144). 



Fig. 142. Terebru'tula 

 Fig 141. Ca'tylus Cuvieri. Defra'nc.v. 



16 What organic remains are found in the chalk formation ? 



